Devices for automatic photographic monitoring of road intersections controlled by traffic light are known. A sensor, e.g. an induction loop imbedded in the road, supplies a signal when a vehicle enters a road intersection monitored by a traffic light. The traffic light supplies a further signal when the traffic light changes to its stop phase. If the vehicle enters the road intersection during the stop phase, a photographic picture is triggered, which records the vehicle and its licence number. Thus, the vehicle can be identified and the violation can be evidentially recorded. In order to improve the evidential value of the photographic registration, several pictures are usually taken one after the other.
Such devices are, for example, described in German Patent 683,658, U.S. Pat. No. 2,871,088, Austrian Patent 225,077, German Patent 1,078,797, an essay in "Polizei, Technik, Verkehr" issue 8 (1965), 269-272 and German Patent 2,365,331.
It is well known that it is possible to measure the speed of a vehicle and to release a photographic picture when exceeding an allowed maximum speed limit. This picture clearly records the vehicle with its licence number.
Austrian Patent 225,077 already mentioned describes in an embodiment a traffic monitoring device having two sensors fixedly spaced from each other in the road. A camera is released and the vehicle is photographed when the time interval between the passing over of the two sensors drops below a predetermined value. A similar device is described in Austrian Patent 246,617.
Furthermore, it is well known that two pictures are taken in fixed time intervals, when the passing vehicle exceeds the allowed maximum speed limit which is signalled by the two sensors arranged in the road and by the evaluation circuit to which the signals from the sensors are applied. A further measuring value of the speed can be obtained from the positions of the vehicle on the two pictures.
Furthermore, it is well known that the speed of a vehicle may be determined by using a Doppler radar. Such a speed monitoring device is described, for example, in U.S. Pat. No. 2,683,071, Swiss Patent 414,210 or Swiss Patent 470,674. In usual photographic speed monitoring devices having Doppler radar, the measured speed is indicated. The vehicle to be monitored is photographed when it exceeds the allowed maximum speed limit and the indication of the actual speed as measured is reflected in the picture (for example German Democratic Patent 66,974).
Practically every one of the devices mentioned above for traffic monitoring comprises arrangements for generating time information, i.e. a clock for indicating the time and a dater indicating the date. This time information is registered together with the picture of the vehicle to be monitored, usually in a manner reflected in the picture (German Democratic Republic Patent 66,974).
Furthermore, it is well known that a sequence of speed measuring values can be generated by means of a Doppler radar while vehicles to be monitored pass the radar beam. These speed measuring values are classified in a memory such that a histogram is obtained, i.e. a frequency distribution of these speed measuring values. Conclusions of passing actions or the like can be drawn from such a histogram. It is also possible to infer the type of the passing vehicle from the histogram, i.e. whether the vehicle is a passenger car or a motor lorry.
Furthermore, for the purpose of traffic count, it is well known that sensors can be imbedded, for example in the form of induction loops, in the road and can detect the number of passing vehicles for statistical purposes.